The following U.S. patents are fully incorporated herein by reference: U.S. Pat. No. 5,523,662 to Goldenberg et al. (xe2x80x9cModular, Expandable and Reconfigurable Robotxe2x80x9d) and U.S. Pat. No. 5,293,107 to Akeel (xe2x80x9cMotorized Rotary Joint and Method of Constructing a Modular Robot Utilizing Samexe2x80x9d).
The present invention relates to modular, expandable and reconfigurable closed chain robotic systems and more particularly to self-locking or ratcheting joints for such systems.
Modular robotic systems are systems which contain many repeated modules having actuators, sensors and computational elements. These modules may be disconnected and reconnected in different arrangements to form a new system enabling new functionalities. There have been a variety of modular reconfigurable systems as there are many aspects of robot systems that can be modular and reconfigurable. These include manual reconfiguration, in which an operator reconfigures the modules, and automatic reconfiguration, in which the robot reconfigures itself or another machine reconfigures the modules. These systems may contain homogeneous or heterogeneous modules.
Modular self-reconfigurable robot systems can also reconfigure or rearrange their own modules. These systems may have many desirable properties, such as versatility (resulting from many possible configurations), robustness (through redundancy and self-repair) and low cost (through batch fabrication). However, one problem with these systems has been the limits of performance of individual actuators within the systems.
Long serial chain robots with many degrees of freedom (DOF), or hyper-redundant robot arms have a variety of applications including inspection robot arms and snake-like locomotion for planetary exploration or search and rescue. Some modular, reconfigurable systems that use many repeated modules use long serial chains as parts of a larger system, much like the tentacles of an octopus. One problem with using serial chains is limited actuation capabilities. Since the number of modules within a chain is variable, the actuation strength required to maneuver the chain varies, and at some point there will be more modules than the system""s actuators"" limits can support. A closed chain is a serial chain with both ends attached to form a loop. Closed chains can resemble long serial chains by flattening the loop.
Typically, in robot arm control, configurations which correspond to singularities in the Jacobian matrix, which describes the ratio of joint velocities of joints in joint space to the velocities of joints in Cartesian space or other work oriented space, are typically avoided to prevent excessive joint velocities or torques. Redundant manipulators have sometimes used the extra DOF to enhance this avoidance. However, in remaining close to such singularities, it is possible to exploit the near infinite mechanical advantage available at the singularity.
Human beings exploit singularities in their walking movement. In taking a forward step, the heel makes contact with the ground and the leg straightens as it begins to take on the weight of the body. When the leg is straight the Jacobian matrix describing the relationship between the joints (hip and knee) and the Cartesian position of the foot becomes singular. Also, the mechanical advantage of the system increases. As the knee approaches straightness, the force that the hamstring muscles can apply parallel to the direction of the leg increases. The effort on the muscles (and thus the amount of energy expended) is correspondingly reduced by the large mechanical advantage.
Similarly, it is possible to obtain large variable mechanical advantage for closed chain serial manipulators with rotational degrees of freedom. Such systems are characterized as having redundancy, which provides additional degrees of freedom, parallelism or closed chain configuration, and at least one configuration where the Jacobean is singular. One additional requirement for this system is a form of lock or brake, which enables the degree of freedom to be made rigid independently of the strength of the actuator. This may be an additional active brake, or a self-locking or non-backdrivable actuator.
Various approaches have employed mechanical advantage to achieve movement. An example of a system that utilizes a fixed mechanical advantage combined with ratcheting is similar to an older style car jack. This device is used to lift a car up by pushing a lever down, thereby lifting the car a small amount and then locking the position so that the motion can be repeated while gaining height. The ratio of the lengths of the lever on each side of the fulcrum determines its fixed mechanical advantage.
Another approach is a closed chain, for example a four bar linkage. In four bar linkages, the device enters a singularity at xe2x80x9ctoggle pointsxe2x80x9d, where three of the joints of the fourbar linkage become collinear so the driving actuator obtains infinite mechanical advantage. This characteristic has frequently been exploited for achieving large forces for things such as clamping devices. However, motions near the toggle point result in very small motions at the point of applied force, which is the reason for enhanced leverage at that point. The leverage is variable depending on how close the system is to the toggle point, theoretically up to infinity.
Increased motion can be achieved by combining the two approaches, ratcheting and variable mechanical advantage with multiple closed chains repeating motions and switching locked joints resulting in a ratcheting action. For very large mechanical advantage, and thus very small motions, the number of motions that must be repeated can be very large. A manual device, such as a hand crank, would not be convenient for such an application, but an automatic device could make very rapid motions and lock switches as necessary to achieve the desired mechanical advantage.
Although useful, the above do not provide the capability of reconfiguring themselves to apply force to an object. An example of such an application is fire and earthquake search and rescue operations, which typically involve collapsed structures with voids and channels formed by the rubble. Very often the topography of the spaces inside these areas are dynamically changing due to further collapse, burning or aftershocks. Typically, a fire fighter must put himself at risk to enter such areas, assuming he can reach them. A device that is capable of a variety of modes of locomotion, whether it is squeezing through holes, or rapidly rolling down hills, or climbing into ducts would be extremely useful not only in reaching areas that humans cannot, but also in reducing the risk to human lives.
In the above application, the system allows the dangerous mission to be performed with minimal risk to people by performing the action at a removed distance. In addition to remote operations, the system can be used to perform functions otherwise dangerous or impossible for human personnel. For example, in a collapsed building it could turn off gas mains and fuses inside the building. This is particularly important in industrial plants in order to shut down operations in areas not accessible by humans due to chemical, fire, or radiation leaks. Here the reconfigurability and versatility of systems of robotic modules are key advantages.
The following disclosures may be relevant and/or helpful in providing an understanding of some aspects of the present invention:
U.S. Pat. No. 5,523,662 to Goldenberg et al., titled xe2x80x9cModular, Expandable and Reconfigurable Robotxe2x80x9d, discloses a robotic system including a robot having at least two manipulators, each having several compact rotary joints. The rotary joints have one input coupling and either one or two output couplings. Each joint is modular including a d.c. brushless motor coupled with a harmonic cup drive and includes position, velocity and torque sensors. Each manipulator may be disassembled and reassembled to assume a multitude of configurations. The modular robot is controlled by an expandable and modular real-time computer control system.
U.S. Pat. No. 5,293,107 to Akeel, titled xe2x80x9cMotorized Rotary Joint and Method of Constructing a Modular Robot Utilizing Samexe2x80x9d, discloses a motorized rotary joint for robots which integrates a joint bearing with a power transmission, such as a planetary type speed reducer. A large central hole permits passing electric and service lines therethrough. The rotary joint includes a built-in rotor and stator arrangement within the same joint housing structure, thus allowing the electric motor to share the same bearing and housing structure with the speed reducer. Preferably, the rotor also carries planets of the reducer and the stator is either integral or coupled to a housing of the reducer. The rotary joint also accommodates an encoder, a circuit board having electronic components thereon and a built-in brake to provide a totally integrated, intelligent rotary joint.
In accordance with one aspect of the present invention, a ratcheting system includes a plurality of modular joints, a plurality of links connected to the modular joints, and a ratcheting device. A control system directs movement of the modular joints and linkages.
In accordance with another aspect of the invention, a controllable ratcheting apparatus operated near a mechanical singularity includes a plurality of modular joints with a plurality of links movably connected to the joints and a ratcheting device. A control system controls movement of the modular joints and their associated links.
In yet another aspect of the invention, there is provided a method for controlling a ratcheting apparatus having a plurality of modular joints, a plurality of links connected to the modular joints, a ratcheting device and a control system. The plurality of joint is configured to form a closed chain. After all of the joints in the closed chain are locked, a first set of joints is unlocked and moved away from a mechanical singularity. At least one of the set of unlocked joints is then locked, and another set of joints is unlocked and moved from a mechanical singularity. The sequence of locking and unlocking selected sets of joints and moving the unlocked joints away from a mechanical singularity is repeated until a desired movement is obtained.